A great deal of interest has been focused on SSLSs, such as LEDs and lasers, and in particular, those that emit light in the blue and deep ultraviolet (UV) wavelengths. These devices may be capable of being incorporated into various applications, including solid-state lighting, biochemical disinfection and detection, high-density data storage, and the like.
Modern SSLSs, such as an LEDs, typically include three major components: an electron supply layer (e.g., an n-type semiconductor layer), a hole supply layer (e.g., a p-type semiconductor layer), and a light generating structure formed between the electron supply layer and the hole supply layer. A number of these SSLSs are used in applications that require a fast on/off switching time of the SSLSs, such as in a nanosecond or sub-nanosecond range. In group III-nitride based SSLSs, such as group III-nitride LEDs, the light turn-off time is limited by the recombination of electron-hole pairs injected into the p-n junctions and the light generating structure regions of the devices. A piezoelectric effect, certain type of traps, and other factors associated with the LEDs, cause the recombination of electron and holes to take a relatively long time after a pumping current has been shut off. A longer recombination of electrons and holes after the pumping current has been shut off translates into a protracted light turn-off time. Deep UV LEDs can also have a relatively long light turn-off time due to the recombination of electrons and holes.
Attempts to improve the fast on/off switching times of the SSLSs have been proposed in order to satisfy applications with faster light modulation (e.g., light being turned off). One approach involves the SSLSs having the device p-n junction regions with an increased defect concentration. A higher defect concentration in the device p-n junction region typically leads to a faster recombination rate of electrons and holes, which translates into faster switching. However, this approach inevitably results in lower light emission and lower LED efficiency. Another approach involves using external light modulators with the SSLSs. However, modulation with an external light modulator involves additional optical loss, power consumption, and leads to significant increase in the overall size, weight and cost of the SSLS devices.